1. Field of the Invention
The present invention relates to a non-radiative dielectric waveguide coupler that is incorporated in a circuit such as a millimeter wave integrated circuit to couple and/or divide high-frequency signals among a plurality of non-radiative dielectric waveguides used as a guide for high-frequency signals.
2. Description of the Prior Art
A non-radiative dielectric waveguide transmits high-frequency signals of a wavelength .lambda. by utilizing a dielectric waveguide interposed between parallel flat conductors maintaining a gap z. Upon setting the gap z between the parallel flat conductors to satisfy a relationship z.ltoreq..lambda./2, it becomes possible to transmit signals preventing the infiltration of noise into the dielectric waveguide from the external side and eliminating the radiation of high-frequency signals to the external side.
The non-radiative dielectric waveguide coupler has heretofore been used for dividing and coupling high-frequency signals (electromagnetic waves) and has a structure which is generally as shown in FIG. 8. Referring to FIG. 8, two dielectric waveguides 12 and 13 are arranged between a pair of parallel flat conductors 11a and 11b (for easy comprehension, the parallel flat conductor 11a is represented by a dot-dash chain line). In FIG. 8, the dielectric waveguides 12 and 13 are both formed in a curved shape, and are so arranged that a predetermined gap x is defined at a position where the two dielectric waveguides 12 and 13 become closest to each other.
In the coupler of the above-mentioned constitution, the high-frequency signals input through a port 12a of the dielectric waveguide 12 partly transmit through the dielectric waveguide 12 and are output from a port 12b, and are partly electromagnetically coupled to the dielectric waveguide 13 at the closest portion and are transmitted toward a port 13b. Thus, the signals are output from the port 12b of the dielectric waveguide 12 and from the port 13b of the dielectric waveguide 13, but are not output from the port 12a of the dielectric waveguide 12 or the port 13a of the dielectric waveguide 13.
On the other hand, the high-frequency signals input through the port 13a of the dielectric waveguide 13 are output from the output port 12b of the dielectric waveguide 12 and from the output port 13b of the dielectric waveguide 13, but are not output from the port 12a of the dielectric waveguide 12 or the port 13a of the dielectric waveguide 13.
The high-frequency signals simultaneously input to the ports 12a and 13a are divided and coupled at a particular ratio, and are output from the ports 12b and 13b.
In the above-mentioned conventional non-radiative dielectric waveguide coupler, however, the distance x at the closest portion seriously affect the characteristics of the coupler. When the dielectric waveguides 12 and 13 comprise NRD guides having a relative dielectric constant of 5, a width of 1 mm and a height of 2.25 mm, the precision of distance x at the closest portion must be controlled to be not larger than 0.1 mm in order to set the dividing ratio practically required for the ports 12b and 13b to be 3 dB.+-.1 dB, i.e., to nearly evenly divide the signals. It is very difficult to arrange the two dielectric waveguides 12 and 13 maintaining a high precision between a pair of parallel flat conductors 11a and 11b, accounting for a major cause that impairs the mass-production. Therefore, the adjustment of positioning during the fabrication drives up the cost of products. There further remains a problem in that the distance x is deviated due to the shock at the time of production or during the use, resulting in a great change in the ratio of division to the ports 12b and 13b.